Trunking communication networks “Analog-to-Digit ... · 1 Trunking communication networks “Analog-to-Digit” Consideration is given to the issued of migration from analog to

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Trunking communication networks “Analog-to-Digit”

Consideration is given to the issued of migration from analog to digital modes of operation in trunking

radio networks. Information materials on individual technical solutions are presented.

Key words: radio communication, trunking, PMR, MRT-1327, DMR, Simulcast.

Introduction

This article will be of interest for specialists with experience in the construction and operation of

trunking communication systems. The information presented here, to our point of view, can be useful

to users planning upgrading their current trunking radio communication networks or construction of

new networks.

In brief, trunking technology can be described as “offering the users of a limited resource

(communication channels) on demand, with a dynamic distribution of the resource between users”.

The key purpose of using trunking technology в PMR is the frequency resource saving.

Today, all trunking communication systems feature the same set of basic functionalities:

-­‐ individual call;

-­‐ group call;

-­‐ calling fixed communication network subscribers;

-­‐ status message service;

-­‐ short message service;

-­‐ arbitrary volume data service.

Nowadays equipment and technology state features a steady tendency to the all-round

implementation of digital technologies. This tendency did not skirt the PMR industry either.

Practically all Manufacturers offer these or those ways to migrated from analog equipment samples to

those digital.

Present on the market are both digital and analog trunking communication systems. However, such

splitting is not fully correct. If the system supports trunking technology, then there is transmission of

signal (digital) information Thus, all trunking communication systems are all digital with regard to

implementing signaling functions! The “analog-to-digit” splitting refers to voice transmission only.

In the users’ environment there is a stable statement that speech quality in digital systems is

admittedly superior than that in analog systems. For PMR radio networks, this statement does not

correspond to reality.

At the dawn of digitization of communication networks, analog signal coding methods were

standardized. Thus, on PSTN use is made of PCM coding at 64 kbit/s. Voice transmission using PCM

within PMR frequency band technically can not be implemented. Digital stream speed corresponding

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to one voice transmission path is 2.4 to 3.6 kbit/s for modern PMR systems. To code voice signal into

digital form use is made of vocoders. Vocoders code only some parameters (amplitude, tone noise,

tone pitch, etc.) of the voice signal and synthesize speech at the receive end. Such coding ensure

excellent characteristic values for signal-to-noise ratio. However, there are substantial voice distortions

due to the coding mechanism proper. Hence, PMR networks analog-to-digit migration of does not

allow improving voice quality.

Then what are the purposes of the analog-to-digit migration? They are different for trunking

communication system users and equipment manufacturers. We see these purposes as follows:

Analog-to-digit migration targets:

For users - to ensure the following: For equipment manufacturers – to ensure the

following:

Higher radio frequency spectrum efficiency. “Design-production-sales” technological cycle integrity.

Security of conversations Lower production costs. Using digital signal processing technology – it provides repeatability of device characteristics and lowers adjustment operations labor content1.

Lower expenses on using fixed communication networks. PMR analog networks, as a rule, make use of TDM technology Digital PMR networks are oriented on using IP-networks.

Creation of additional possibilities to obtain profit at the expense of designing and implementation of additional applications.

Provide access to the trunking communication network for various automation equipment complexes.

Prepare for phasing out analog trunking communication equipment2

1 For the sake of truth, it is worth noting that if the production process becomes less extravagant, then the process of designing new solutions and equipment samples, vice versa, becomes substantially more expensive 2 Manufacturers will remove current equipment from production and cease its technical support.

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In spite of substantial differences in the suppliers and manufacturer, it should recognized that

migration from analog PMR trunking systems to digital systems is inevitable.

What migration ways do we consider correct? This article suggests to consider one of the migration

ways. Let’s consider MPT-1327 systems as most popular analog trunking communication networks,

whereas DMR systems - as digital networks. DMR standard is the only digital standard permitted for

use in the PMR system traditional frequency bandwidths on the Russia’s territory.

Technical solutions for the “analog-to-digital” migration The information presented below refers to solutions offered by LLC “MPT-Service Project”. These

technical solutions are not “the only possible”. Other equipment Manufacturers, system integrators can

offer their own versions.

The migration activities set depends on the radio communication network structure. The migration

activities in question are applied to upgrading of radio communication network built using Fylde

Micro or “AMGA-1327” infrastructure.

“AMGA-1327” radio communication network structure designed by LLC “MPT-Service

Project”

“AMGA-1327” radio communication network structure is defined by the controllers equipment type.

Channel, site and region controllers are built using Fylde Micro (Great Britain) completing part. The

structure is based on a radial-zone topology. Provision is made for measures on improving resistance

of the equipment to failures: failure of one element does not result in total loss of communication, but

only lowers the system functionality. Fig. 1 shows the system functional diagram.

Fig.1 “AMGA-1327” trunking communication system functional diagram

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“Analog-digit” migration activities

The migration first step includes replacement of transponders equipment. The current transponders

support only analog mode. Transponder offered for replacement support both analog and digital

(DMR) mode. This replacement does not affect functionality of the current analog network but creates

a technical background for migration.

The migration second step can be carried out using one of the two methods: a “revolutionary” and an

“evolutionary”. When using a “revolutionary” method, after all the radio communication system

transponders are replaced and configured for operation in the DMR mode. It is worth noting that

“AMGA-DMR-BS-160-450” transponders are fully equipped for operation in the DMR mode.

Trunking network operation is effected in full compliance with the DMR Tier II specifications. Radio

communication system functional diagram for the “revolutionary” version is shown in Fig. 2

Fig. 2 “Revolutionary” method functional diagram

When using the "evolutionary" method only some repeaters are switched over to DMR mode. Thus,

there are two subsystems MPT-1327 and DMR Tier III - operating in one and the same network

simultaneously. When using an “evolutionary” method, there is a possibility to split in time the

migration activities and the related costs. Besides, provision is made for terminal equipment fleet

operation. Fig. 3 shows radio communication system functional diagram for the “evolutionary”

version.

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Fig. 3. “Evolutionary” method functional diagram

An important step in the migration is the replacement of subscriber terminals. Currently terminal

equipment market has already presented samples capable of operation in a DMR + MPT-1327 radio

communication network combined structure.

The migration version considered can technically be implemented owing to unique characteristics of

“AMGA-DMR-BS-160-450” transponders (Fig. 4).

Fig. 4. “AMGA-DMR-BS-160-450” equipment appearance

Technical characteristics of equipment “AMGA-DMR-BS-160-450”

“AMGA-DMR-BS-160-450” repeaters are manufactured by LLC “MPT-Service Project” using

completing parts and software manufactured by “Radio Activity” (Italy). The transponders are capable

of operation in the following modes:

-­‐ Analog;

-­‐ Simulcast analog;

-­‐ DMR Tier II;

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-­‐ DMR Tier II Simulcast;

-­‐ DMR Tier III trunking;

-­‐ DMR Tier III trunking Simulcast;

Not all users are familiar with the Simulcast technology specifics. Let’s consider the basic functioning

principles of such radio networks by the example of operation of the Simulcast single-channel radio

communication system.

Transponders are arranged on the terrain and interconnected using land communication links. One of

the transponders is configured as a master station, whereas the rest transponders are configured as

slave ones. All transponder, including those with their coverage interleaving, make use of only one

pair of frequencies. Subscriber terminal signal can be received by several receivers at the same time.

All the network receivers on receiving the signal, direct it to the master station. Master station

controller serves as the received signals voter (selecting the best signal). The selected signal is directed

to all the network transmitters. Special provision is made to synchronize transmitters working

frequencies, synchronize radiation time and provide similarity of the signal transmit channels

characteristics throughout the fixed communication network. Owing to these measures, the terminal

can receive the signal from several transmitted simultaneously, without degrading the signal quality.

The main advantages of Simulcast networks lie in the economy of the frequency resource and

simplicity of the network scaling. Roaming feature in Simulcast networks is integrated by default as

distinguished from other technologies of creating geographically-distributed radio communication

networks. Fig. 5 shows the Simulcast network layout.

Fig. 5. Simulcast network layout

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“AMGA-DMR-BS-160-450” equipment set features the following specifics:

-­‐ Space diversity reception is implemented;

-­‐ Provision is made for comprehensive facilities providing interaction with external

communication networks;

-­‐ DMP Tier II mode allows construction of bridged taps based on DMR radio channels.

The advisability of the “analog-to-digit” migration shall be substantiated. Currently, migration is not

advisable or is impossible due to financial issues. MPT-1327 analog systems approved themselves as a

reliable solution for construction of PMR trunking networks. To our opinion, such networks will be

operated and constructed for the nearest decade to come. Functional capabilities of MPT-1327

trunking networks can be substantially expanded by implementing up-to-date application. Data

transmission feature in the MPT-1327 “analog” network are not less developed compared to that in the

DMR networks. Thus, information exchange speed in transmitting arbitrary format data and in using

traffic channel in MPT-1327 networks can be twice as high compared to that in DMR. However, using

the wide range of the MPT-1327 capabilities requires special technical personnel: engineers –

specialists in radio engineering with experience in software programming. No higher educational

institution trains such specialists. On the contrary, DMR designers provide tools comprehensible to

most programmers. It is not coincidental that today we observe real boom conditions in the

development of various applications for DMR Tier II networks.

Information on applications developed by LLC “MPT-Service Project” for MPT-1327 radio

communications networks

LLC “MPT-Service Project” developed the following applications for implementation on AMGA-

1327 equipment radio networks:

− “Track” hardware/software complex.

The complex is designed to perform transport monitoring functions. Used as positioning data source

are GLONASS receivers The onboard monitoring set features an open architecture and makes it

possible to connect external signals via CAN and RS-485 interfaces. Provision is made for connection

of the fuel level monitoring equipment. Data transmission is based on using SDM procedures. Use is

made of the client/server data acquisition and processing system. Reports preparation procedures are

made in the form of separate applications. One of the applications has no countertypes. The application

makes it possible to construct a real radio coverage map based on the data processing statistics.

− Conversations recording system

The system is capable of recording voice call. Each call is identified by time and terminal number that

initiated the call/ Access to data is ensured via WEB-interface.

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− Data transmission controller

The controller is designed and manufactured in compliance with the MAP-27 specifications. Provision

is made for using both SDM and arbitrary format data transmission.

Conclusion

So, the basis for the “analog-to-digit” migration is as follows:

-­‐ Frequency resource deficiency, expansion of the current network;

-­‐ Necessity in ensuring stealthiness of conversations;

-­‐ Impossibility of using fixed TDM communication channels.

It is appropriate to construct new trunking communication networks supporting 2 operation modes -

MPT-1327 and DMR. Thus provision will be made for the network reliable operation inherent in

MPT-1327 systems, and engineering basis will be prepared for migration to the digital technology. I

should not be forgotten that DMR technology is a young one and DMR implementation imply risks.

DMR networks implementation risks are related to the incomplete process of protocols

standardization, possible incompatibility (at the protocols level) of equipment by different

manufacturers, availability of mistakes both in the base and terminal equipment.

In the short term, PMR networks “analog-to-digit” migration is and actual task only for some

radio communication networks. This activity involves substantial expenses and shall be planned

with the account of sufficient grounds.

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Glossary:

PMR Professional mobile radio

MPT-1327 Signaling protocol for trunking radio networks with a dedicated control

channel. Developed by Ministry of Post and Telegraph (Great Britain)

DMR Digital Mobile Radio. PMR standard. Developed by ETSI (European

Telecommunications Standards Institute)

Simulcast PMR technology. Provides for construction of the system based on several

base station operating synchronously using one pair of radio frequencies

PCM Pulse-code modulation

TDM Time Division Multiplexing

BS Base station

IP Internet Protocol - provides routing in data transmission systems, namely in

Internet

DMR Tier II DMR standard specifications set specifying operation of dispatcher

networks, without trunking feature control

DMR Tier III DMR standard specifications set specifying trunking networks operation

GLONASS Global navigation system

CAN Controller Area Network - a standard defining controller network

functioning procedure. Widely used in automobile industry

RS-485 Recommended Standard 485 – a standard for acynchronous interface.

Developed by two associations: EIA — Electronics Industries Association

and TIA — Telecommunications Industry Association

SDM Short Data Message. As a rule, format of these messages is included in the

trunking communication protocol description

MAP-27 Data transmission protocol in MPT-1327 trunking radio networks

communication